Biologically active agents such as nutritional supplements, hormones, and a variety of pharmaceutical preparations, which will generally be referred to as “drugs’ are typically provided in oral (liquids or solids) or injectable dosage formulations, however there are many disadvantages associated with this type of administration.
Many of the ingredients are degraded within the gastrointestinal (GI) tract or undergo first-pass metabolism in the liver. In addition, there exists a segment of the population who experience difficulty swallowing pills or are unable to tolerate any solids.
During the past three decades, however, formulations that control the rate and period of drug delivery (e.g., time-release medications) and target specific areas of the body for treatment have become increasingly common and complex. Some have provided solutions to the problem of administering different types of drugs but there are still a large number of medications that do not achieve maximum pharmaceutical effect because they do not reach the intended tissue targets either fast enough or in high enough concentrations.
The potency and therapeutic effects of many drugs are limited or reduced because of the partial degradation that occurs before they reach a desired target in the body. Further, injectable medications could be made less expensively and administered more easily if they could simply be dosed by other routes such as the oral mucosa, the pulmonary mucosa or through the vaginal and intestinal tract. However, this improvement cannot happen until methods are developed to safely shepherd drugs through these specific areas of the body, where different physiological environments (e.g. low pH values in the stomach) can destroy a medication or where absorption is not rapid or complete, or through an area where healthy tissue might be adversely affected.
Transmucosal routes of drug delivery offer distinct advantages. Of the various routes, the mucosal linings of the nasal passages and the oral cavity are the most attractive. Although the nasal route has reached commercial success with several drugs, such as with allergy medications, potentially serious side-effects, such as irritation and possibly irreversible damage to the ciliary action of the nasal cavity from chronic application, have deterred health professionals from recommending their long-term use.
Within the oral cavity, there are three generally recognized routes of administration of a biologically active agent. Local delivery is mainly limited to applications regarding disruptions occurring within the oral cavity itself, such as a canker sore. Sublingual delivery is achieved through the mucosal membranes lining the floor of the mouth. This route provides rapid absorption and has reached commercial status with biologically active agents such as nitroglycerin, which is placed under the tongue. Because of the high permeability and the rich blood supply, transport via the sublingual route results in a rapid onset of action, providing a delivery route appropriate for highly permeable drugs with short delivery period requirements and an infrequent dosing regimen. The negative however, is that it produces a saliva wash (swallowing) and in the case of nitrolinqual it has been found to cause headaches as a result of administering excess of the drug needed to accomplish it's task.
The third generally recognized route is the buccal mucosa. This area encompasses the mucosal membranes of the inner lining of the cheeks. This area also has a rich blood supply, is robust, and provides a short cellular recovery time following stress or damage. Although the buccal mucosa is less permeable than the sublingual area, the expanse of smooth and relatively immobile mucosa provide a highly desirably absorption pathway for sustained-release and controlled-release delivery of biologically active agents. As with other transmucosal routes of administration, two major advantages include avoiding hepatic first-pass metabolism and pre-systemic elimination within the GI tract.
One of the major disadvantages associated with buccal mucosa delivery of a biologically active agent has been the relatively low passage of active agents across the mucosal epithelium, thereby resulting in low agent bioavailability, which translates into a substantial loss usable active agent within each dosage. Various permeation and absorption enhancers such as POLYSORBATE-80, Sorbitol, and phosphatidylcholine have been explored to improve buccal penetration. Studies have indicated that the superficial layers and protein domain of the epithelium may be responsible for maintaining the barrier function of the buccal mucosa (Gandhi and Robinson, Int. J. Pharm. (1992) 85, pp129-140).
Additionally, it is known that use of a permeation enhancer can increase the passage of a biomolecule. Furthermore, studies have suggested the feasibility of buccal delivery of even a rather large molecular weight pharmaceutical (Aungst and Rogers, Int. J. Pharm. (1989) 53, pp227-235).
A further area of investigation includes the use of bioadhesive polymers in buccal delivery systems. Bioadhesive polymers have been developed to adhere to a biological substrate in order to maintain continual contact of an agent with the site of delivery. This process has been termed mucoadhesion when the substrate is mucosal tissue (Ch'ng et al., J. Pharm. Sci. (1985) 74, 4, pp399-405).
The goal of all drug delivery systems is to deploy medications intact to specifically targeted parts of the body through a medium that can control the therapy's administration by means of either a physiological or chemical trigger.
To achieve this goal, a number of researchers have turned to advances in micro and nanotechnology. One prominent area of endeavor is the production of so-called “nanoparticles” which act as chemical or physical “carriers” of drugs.
During the past decade, novel polymeric microspheres, polymer micelles, and hydrogel-type materials have been shown to be effective in enhancing drug targeting specificity, lowering systemic drug toxicity, improving treatment absorption rates, and providing protection for pharmaceuticals against biochemical degradation. These are all goals of drug delivery. In addition, several other experimental drug delivery systems show signs of promise, including those composed of biodegradable polymers, dendrimers (so-called star polymers), electroactive polymers, and modified C-60 fullerenes (also known as “buckyballs.)
Polymer drug delivery systems are based on “carriers” which are composed of mixing polymeric chemical compounds with drugs to form complex, large molecules, which “carry” the drug across physiological barriers.
Illustrative examples of these polymeric compounds are poly(ethylene-glycol)-poly(alpha, beta-aspartic acid), carboxylates, and heterobifunctional polyethylene glycol, in addition to others.
Another type of nanotechnology revolves around the use of “hydrogels” as carriers of drugs. The principle behind this technology is to use a chemical compound which traps a drug and then releases the active compound by “swelling” or expanding inside of specific tissues, thus allowing a higher concentration of the drug in a biodegradable format. Hydrogels are very specialized systems and are generally formulated to meet specific needs for the delivery of individual drugs.
During the past two decades, research into hydrogel delivery systems has focused primarily on systems containing polyacrylic acid (PAA) backbones. PAA hydrogels are known for their super-absorbency and ability to form extended polymer networks through hydrogen bonding. In addition, they are excellent bioadhesives, which means that they can adhere to mucosal linings within the gastrointestinal tract for extended periods, releasing their encapsulated medications slowly over time.
One example of the complexity of these systems is a glucose-sensitive hydrogel that could be used to deliver insulin to diabetic patients using an internal pH trigger. This system features an insulin-containing “reservoir” formed by a poly[methacrylic acid-g-poly(ethylene glycol)]hydrogel membrane into which glucose oxidase has been immobilized. The membrane itself is housed between nonswelling, porous “molecular fences”.
Although these approaches are the focus of intense research, other processes are also under consideration, including aerosol inhalation devices, transdermal methodologies, forced-pressure injectables, and biodegradable polymer networks designed specifically to transport new gene therapies.
Another method to formulate drugs for delivery has been the use of nanosuspensions of drugs for reducing size and creating uniform suspensions. The use of commercial devices such as mill processors, microfluidizers and homogenizers has allowed the formulation of nanosuspensions of various substances. Nanosuspended drugs can also be wrapped in liposomes or made into micellar mixtures by mixing the drug preparations with appropriate chemical compounds.
Prior artisans have explored a variety of avenues in an effort to produce a viable and efficient means for buccal mucosal delivery. Such avenues include the use of liposomal carriers to enhance uptake or facilitate the delivery of a product; decreasing the particle size of microspherical carriers, or employing a physical matrix, such as a sponge, to hold a medicinal product at the buccal area.
What is lacking in the art is a method for increasing the bioavailability of a biologically active agent, which may be administered via various routes, but particularly with regard to administration via the buccal mucosa; and a stable product useful for carrying out the method.